Sensor for automatic doors

ABSTRACT

Cameras  51, 52  take images of a predetermined area around a door. A distance measurement unit  53  measures the distance to each object in the taken images. Based on the measured distance, a floor detection unit  54  detects a floor, and an object height/position detection unit  55  detects the height and position of any object other than the floor. A door position detection unit  56  and the door position identification unit  57  specify the position of the door (i.e. open or closed) on the images. A judgement unit  58  judges the presence or absence of an object which is neither the floor nor the door. If an object other than the floor and the door is observed in the images, an output unit  59  produces an object detection signal, so that the door is kept in an open state.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a sensor for automatic doors. In particular, the present invention concerns measures to conduct an object detection operation in a predetermined area without fail, thereby enhancing the reliability of the opening/closing action of automatic doors.

[0002] With respect to an automatic door which opens and closes along a track, an object detection range is usually set on the interior and the exterior of the doorway, and objects in the respective detection range are detected by an activation sensor. The activation sensor generally includes sensor mats, ultrasonic sensors and passive/active infrared sensors. On detecting entry of an object within the respective detection range, the activation sensor is turned on and operates to open the door.

[0003] In addition to the activation sensor, an auxiliary safety sensor is disposed in the vicinity of the track of the door, between the interior and exterior detection ranges. As disclosed in Japanese Patent Laid-open Publication No. 2000-320243, the auxiliary safety sensor makes use of light beams (e.g. infrared rays). Typically, the auxiliary safety sensor can be classified into the three types.

[0004] The first type of auxiliary safety sensor is shown in FIG. 6 (FIG. 6(A) is a front view of an automatic door. FIG. 6(B) is a sectional view taken along the line B-B in FIG. 6(A)). As illustrated, beam sensors are mounted on a pair of posts 62, 62 which stand on both sides of a doorway 61. Transmitters 63, 63 on one of the posts locate face to face with receivers 64, 64 on the other post (The structure in FIG. 6 employs two beam sensors, each of which is composed of a transmitter 63 and a receiver 64). In each sensor, when a light beam is emitted from the transmitter 63 towards the receiver 64 and interrupted by a person or the like, the receiver 64 fails to receive the light beam. The sensor regards this condition as the presence of an object near the track of doors 65. Based on this recognition, the auxiliary safety sensor holds the doors 65 open, even when the activation sensor is turned off.

[0005] The second type of auxiliary safety sensor is shown in FIG. 7 (FIG. 7(A) is a front view of an automatic door. FIG. 7(B) is a sectional view taken along the line B-B in FIG. 7(A)). As illustrated, a transmitter 63 and a receiver 64 are mounted at the end of a first door 651, whereas mirrors 71, 71 are equipped at the end of a second door 652 in order to reflect the light emitted from the transmitter 63 back to the receiver 64. Similar to the first prior art structure, when a light beam is emitted from the transmitter 63 and interrupted by a person or the like, the receiver 64 fails to receive the light beam. The sensor regards this condition as the presence of an object near the track of the doors 651, 652. Based on this recognition, the auxiliary safety sensor holds the doors 651, 652 open, even when the activation sensor is turned off. Such auxiliary safety sensor is disclosed, for example, in Japanese Patent Laid-open Publication No. H6-138253.

[0006] The third type of auxiliary safety sensor is shown in FIG. 8. An ultrasonic sensor 82 is built in a transom 81 above a doorway 61 and produces ultrasonic waves toward and around the track of doors 65. In FIG. 8, the detection area of the ultrasonic sensor 82 is defined by a dash-dotted line. According to this sensor, a sensor signal from the ultrasonic sensor 82 is considered valid, only when the doors 65 are fully open. On the other hand, when the doors 65 are fully closed or in the course of closing, any sensor signal from the ultrasonic sensor 82 is considered invalid. This principle prohibits the sensor 82 from wrongly detecting the closing doors 65 as a person or other object, so that the doors 65 are not made open at unnecessary occasions.

[0007] However, these conventional sensors present various problems as mentioned below.

[0008] As for the first type of auxiliary safety sensor (FIG. 6), the detectable object is limited to an object which stands at or passes through the height and position where either pair of the transmitters 63, 63 and the receivers 64, 64 is mounted (at the height indicated by dash-dotted lines). In this case, the sensor fails to detect a small object locating on the track (an object 66 depicted by an imaginary line i in FIG. 6). Consequently, the doors 65, 65 close as soon as the activation sensor is turned off, catching the object 66 between the doors 65, 65. As another problem, because the transmitters 63, 63 and the receivers 64, 64 are mounted on the posts 62, 62, it is impossible to direct the beams vertically above the track. Again, the sensor may fail to detect an object which lies on the track. In other words, if an object 67 locates at a position depicted by an imaginary line j in FIG. 6, the sensor cannot detect the object 67, which is high enough for the height and position of the beams but which fails to block the beams. Furthermore, installation of the transmitters 63, 63 and the receivers 64, 64 involves complicated arrangement of the wiring through the inside of the posts 62, 62.

[0009] The second type of auxiliary safety sensor (FIG. 7) can direct the beam vertically above the track, thereby being capable of detecting an object which lies on the track. However, as with the first type of sensor, the detectable object is limited to an object which stands at or passes through the height and position of either of the beams. Referring to FIG. 7, the sensor fails to detect a small object 66 laid on the track, as depicted by an imaginary line i. Moreover, installation of the second prior art sensor is more complex than that of the first one, because the transmitter 63 and the receiver 64 are mounted on the door 651 and need to have the wiring arranged through the inside of the door 651.

[0010] The third type of auxiliary safety sensor (FIG. 8) solves the trouble of arranging the wiring through the inside of the posts 62, 62 or the doors 65, 65 and improves its installation workability. On the other hand, this sensor has a different problem, because a signal from the ultrasonic sensor 82 is invalidated as soon as the doors 65, 65 start the closing action. Namely, once the doors 65, 65 start to close, it is impossible to detect a person coming from an area which is not covered by the activation sensor.

[0011] As mentioned above, none of the conventional sensors for automatic doors provides sufficient reliability in object detection. Therefore, there have been considerable demands for a sensor for automatic doors which can ensure satisfactory reliability in object detection.

SUMMARY OF THE INVENTION

[0012] The present invention is made in view of these problems. An object of the present invention is to provide a sensor for automatic doors which can ensure detection of an object in a predetermined area around an automatic door, thereby enhancing the reliability of the opening/closing action by the automatic door.

[0013] In order to accomplish this object, the present invention intends to improve the reliability of the object detection operation in the following manner. According to the present invention, image pickup means such as a CCD camera takes an image of a predetermined area around the door. In this image, the distance between the image pickup means and each object is measured. Based on the measured distance, the sensor identifies the presence or absence of an object which excludes the background object (e.g. a floor, a wall) and the door.

[0014] A sensor for automatic doors corresponding to claim 1 (hereinafter mentioned as Invention 1) is composed of image pickup means, distance measurement means, object identification means and output means. The image pickup means is capable of taking an image of a predetermined area around a door. The distance measurement means measures a distance between the image pickup means and each object observed in the taken image of the predetermined area, on receiving an output from the image pickup means. The object identification means identifies the presence of an object which is neither a background object nor the door, on receiving an output from the distance measurement means. Firstly, each object for which the distance from the image pickup means is measured is identified either as a background object or as an object other than the background object, based on the measured distance. Secondly, the object other than the background object is identified either as the door or as an object other than the door. The output means outputs an object detection signal, on receiving an output from the object identification means. This object detection signal is produced, with a proviso that the object which is neither the background object nor the door is observed in the taken image of the predetermined area.

[0015] According to these features, once the image pickup means takes an image of the predetermined area around the door, the distance measurement means measures the distance between the image pickup means and each object observed in the image. Based on this information, the object identification means identifies the presence or absence of an object excluding the background object and the door. If such object is present, the output means produces an object detection signal. This signal serves, for example, to keep the door in the fully open state. Thus, in order to identify the presence or absence of the object to be detected (e.g. a person), this sensor relies on the image of the predetermined area around the door. As a result, compared with the beam sensors, the sensor of Invention 1 can have an extensive detectable range. Further regarding the identification of the presence or absence of the object, the sensor considers the information except the one relating to the door. Hence, even when the door is observed in the image, the sensor ensures a reliable object detection operation, without mistaking the door for a person or the like.

[0016] A sensor for automatic doors corresponding to claim 2 (hereinafter mentioned as Invention 2) is composed of image pickup means, distance measurement means, floor detection means, object height/position detection means, door position detection means, door position identification means, judgement means and output means. The image taking means is capable of taking an image of a predetermined area which covers a track of a door. The distance measurement means measures a distance between the image pickup means and each object observed in the taken image of the predetermined area, on receiving an output from the image pickup means. The floor detection means detects a floor and a height and position of the floor, on receiving an output from the distance measurement means. At this stage, the floor is detected from any object for which the distance from the image pickup means is measured. The object height/position detection means detects a height and position of an object other than the floor, on receiving outputs from the distance measurement means and the floor detection means. It should be understood that the object other than the floor is an object which is observed in the image taken by the image pickup means covering the predetermined area and which locates at a different height and position relative to the height and position of the floor. The door position detection means is capable of detecting whether the door is in an open position or a closed position along the track. The door position identification means identifies a position of the door on the image, on receiving an output from the door position detection means, based on the detected position of the door. The judgement means judges whether the object which is observed in the taken image of the predetermined area and which is other than the floor is the door or an object other than the door, on receiving outputs from the object height/position detection means and the door position identification means. The output means outputs an object detection signal, on receiving an output from the judgement means. The object detection signal is produced, with a proviso that the object which is neither the floor nor the door is observed in the taken image of the predetermined area.

[0017] Similar to Invention 1, these features realize a detection operation in the following manner. Once the image pickup means takes an image, the sensor of Invention 2 obtains information on the distance between the image pickup means and each object observed in the image. Based on the information, the sensor judges the presence or absence of the object other than the floor and the door. Therefore, the resulting sensor can have an extensive detectable range and perform a reliable object detection operation, without mistaking the door for a person or the like. In particular, Invention 2 specifies the operation for distinguishing the floor (the background object) from any object other than the floor, and also specifies the operation for identifying the door position. These features serve to improve the practicality of the sensor for automatic doors.

[0018] A sensor for automatic doors corresponding to claim 3 (hereinafter mentioned as Invention 3) features a specific operation of the output means for producing the object detection signal. In detail, the sensor of Invention 1 or Invention 2 is associated with means for controlling an open/close drive of the door along the track. In this sensor, the output means is arranged to be capable of outputting the object detection signal to the door drive control means, such that the object detection signal outputted to the door drive control means causes the door to open fully. These features prevent accidental closure of the door, while a person or the like is present near the track of the door. Eventually, the features of Invention 3 enhance the reliability in the opening/closing action of the automatic door.

[0019] Sensors for automatic doors, corresponding to claim 4 and claim 5 (hereinafter mentioned as Invention 4 and Invention 5, respectively), are featured by specific operations of the distance measurement means for measuring the distance between the image pickup means and each object. With respect to any of Invention 1 to Invention 3, the sensor of Invention 4 employs image pickup means which has a plurality of image pickup elements. In this sensor, the distance measurement means is arranged to measure the distance to each object, by stereo image processing which utilizes parallax of images taken by these image pickup elements.

[0020] Further, with respect to any of Invention 1 to Invention 3, the sensor of Invention 5 employs image pickup means which has a variable focus lens. In this sensor, the distance measurement means is arranged to measure the distance to each object, based on the degree of focus on the object which is observed in the image taken by the image pickup means.

[0021] These features enable accurate measurement of the distance between the image pickup means and each object. In particular, the sensor of Invention 5 can simplify the structure of the image pickup means, because it requires no more than one image pickup element.

[0022] Sensor for automatic doors, corresponding to claim 6 and claim 7 (hereinafter mentioned as Invention 6 and Invention 7, respectively), are featured by specific operations of the door position detection means for detecting the position of the door (i.e. open or closed). With respect to Invention 2, the sensor of Invention 6 is associated with means for controlling an open/close drive of the door along the track. This door drive control means produces an output signal corresponding to the position of the door. In this sensor, the door position detection means is arranged to be capable of receiving the output signal from the door drive control means, and to detect whether the door is in the open position or the closed position, based on the received output signal. By way of illustration, the door drive control means is arranged to output a pulse signal, the number of which depends on the position of the door (i.e. open or closed). The door position detection means is arranged to receive the pulse signal and to detect whether the door is in the open position or the closed position, based on the number of pulses.

[0023] Also with respect to Invention 2, the sensor of Invention 7 arranges the door position detection means to detect whether the door is in the open position or the closed position, based on the image taken by the image pickup means. For example, the door position (i.e. open or closed) is detected in accordance with the position and angle of the edge of the door in the image.

[0024] These features enable accurate detection of the door position (i.e. open or closed). In particular, the sensor of Invention 7 can simplify the structure of the automatic door as a whole, by omitting a sensor or the like specially arranged to detect whether the door is in the open position or the closed position.

BRIEF DESCRIPTION OF THE DRAWINGS

[0025]FIG. 1 is a perspective view showing an automatic door and around a doorway of the automatic door, according to an embodiment of the present invention.

[0026]FIG. 2 is a block diagram showing the constitution of an auxiliary safety sensor, according to an embodiment of the present invention.

[0027]FIG. 3(A) represents an image taken when the door is fully open.

[0028]FIG. 3 (B) represents an image taken when the door is fully closed.

[0029]FIG. 4 is an illustration describing an operation for measuring the distance between the cameras and each object.

[0030]FIG. 5 is a view equivalent to FIG. 1, in which the sensor for automatic doors according to the present invention combines the functions of an auxiliary safety sensor and an activation sensor.

[0031]FIG. 6 relates to the first type of conventional auxiliary safety sensor, wherein

[0032]FIG. 6(A) is a front view of an automatic door equipped with the auxiliary safety sensor, and

[0033]FIG. 6(B) is a sectional view taken along the line B-B in FIG. 6(A)

[0034]FIG. 7 relates to the second type of conventional auxiliary safety sensor, wherein

[0035]FIG. 7 (A) is a front view of an automatic door equipped with the auxiliary safety sensor, and

[0036]FIG. 7(B) is a sectional view taken along the line B-B in FIG. 7(A).

[0037]FIG. 8 describes the third type of conventional auxiliary safety sensor.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0038] Embodiments of the present invention are hereinafter described with reference to the drawings. In these embodiments, the sensor for automatic doors according to the present invention is applied as an auxiliary safety sensor.

[0039]FIG. 1 is a perspective view showing an automatic door and around a doorway of the automatic door, concerning this embodiment. As shown, the automatic door used in this embodiment is a bi-parting door which has two door segments 1, 1 movable in opening/closing directions (movable in horizontal directions) along a track T (shown by a broken line in FIG. 1). A detection area of an activation sensor (not shown) is set on the interior and the exterior of a doorway 2. When a person or the like enters the detection range, the activation sensor detects its presence and produces an object detection signal. This signal is sent to an automatic door controller 4 (door drive control means) housed in a transom 3. On receiving the object detection signal, the automatic door controller 4 starts a driving motor of a door opening/closing mechanism (not shown) in order to open the door segments 1, 1. Since the opening/closing mechanism of the door segments 1, 1 is well known in the art, its description is omitted herein. As for the activation sensor, a common ultrasonic or pyroelectric sensor is adoptable.

[0040] The transom 3 mounts an auxiliary safety sensor 5, which is the feature of the present embodiment as detailed below.

[0041]FIG. 2 is a block diagram showing the general constitution of the auxiliary safety sensor 5. As shown, the auxiliary safety sensor 5 is composed of two cameras 51, 52 (each having a built-in image pickup element such as CCD) as image pickup means, a distance measurement unit 53 as distance measurement means, a floor detection unit 54 as floor detection means, an object height/position detection unit 55 as object height/position detection means, a door position detection unit 56 as door position detection means, a door position identification unit 57 as door position identification means, a judgement unit 58 as judgement means, and an output unit 59 as output means.

[0042] The cameras 51, 52 are contained in a sensor casing 5A, with their optical axes oriented parallel to each other. Incidentally, the optical axes of the cameras 51, 52 may not necessarily be parallel, but may be oriented in slightly different directions from each other. The sensor casing 5A is mounted on the transom 3, such that image pickup directions of the cameras 51, 52 are oriented at predetermined elevation angles relative to the vertically downward direction. Thus, each of the cameras 51, 52 can take an image of a prescribed image pickup area including the track T of the door segments 1, 1 (the hatched area in FIG. 1). FIG. 3(A) represents an image taken when the door segments 1, 1 are fully open. FIG. 3(B) represents an image taken when the door segments 1, 1 are fully closed.

[0043] The distance measurement unit 53 receives information which relates to images taken by the cameras 51, 52. Then, the unit 53 measures the distance between the cameras 51, 52 and each object in the images, by so-called stereo image processing. To be specific, between the image taken by the camera 51 and the image taken by the camera 52, the unit 53 measures displacement (i.e. “parallax”) of each object observed in both images. The distance between the cameras 51, 52 and the object is measured according to the following formula (1):

K=2af/S  (1)

[0044] wherein K represents the distance between the cameras 51, 52 and an object, 2a indicates the spacing between the cameras 51, 52, f represents the focus distance of the lenses of the cameras 51, 52, and S represents the parallax.

[0045] In this embodiment, “the object for which the distance K from the cameras 51, 52 is measured” encompasses all objects which are present in the above-defined image pickup area, including not only a person and like object but also a floor 6 (the background object in the sense of the present invention), the door segments 1, 1, etc.

[0046] Regarding the general stereo image processing, the distance between the cameras 51, 52 and each object is obtained as the distance of a straight line which extends orthogonally to the plane L in FIG. 4 (the plane L is a plane orthogonal to the image pickup direction of the cameras 51, 52), namely, as a linear distance parallel to the image pickup direction of the cameras 51, 52. To be specific, the distance from the cameras 51, 52 to the floor 6 is measured as L1. In the presence of an object 7 (depicted by an imaginary line in FIG. 4), the distance from the cameras 51, 52 to the object 7 is measured as L2. To obtain the actual distance between the cameras 51, 52 and each object (L3 is the actual distance from the cameras 51, 52 to the floor 6, and L4 is the actual distance from the cameras 51, 52 to the object 7.), the distance measured by the foregoing computation is corrected by a trigonometric function. In some cases, the measured distance can be directly used as the actual distance without a significant error. Then, it is possible to omit the distance correction and go to the next process.

[0047] After the distance measurement unit 53 measures the distances between the cameras 51, 52 and the objects (the floor 6, the door segments 1, 1, a person or like object), the floor detection unit 54 recognizes the floor 6 among these objects, and detects the height and position of the floor 6. To be specific, in the test operation of the automatic door, after the distance measurement unit 53 measures the distances from the cameras 51, 52 to all objects, the floor detection unit 54 recognizes, as the floor 6, an object which locates vertically under the cameras 51, 52. To be more specific, in the test operation of the automatic door, the area vertically under the cameras 51, 52 is cleared of any object except the floor 6. In this situation, the distance measurement unit 53 measures the distance to an object which is present vertically under the cameras 51, 52, and also detects a point which locates vertically thereunder in the images (the point P1 in FIG. 3 and FIG. 4). According to the information, any object which locates at the same height and position as the point P1 is recognized as the floor 6 by the floor detection unit 54. In this manner, the floor detection unit 54 recognizes the positional relationship between the cameras 51, 52 and the floor 6, such as the mounting height and position of the cameras 51, 52 relative to the floor 6 (i.e. the height and position of the floor 6) and the elevation angle of the cameras 51, 52.

[0048] The object height/position detection unit 55 receives output signals from the distance measurement unit 53 and the floor detection unit 54. Then, the unit 55 detects the height and position of all objects, except the floor 6, which are observed in the images taken by the cameras 51, 52. In the unit 55, any object which locates at the same height and position as the position-recognized floor 6 is recognized as the floor 6. Based on this recognition, the unit 55 fetches information which solely relates to any object locating at a different height or position relative to the floor 6 (any object whose height and position is not identical to that of the floor 6), and acquires the information on the height and position of the object.

[0049] The door position detection unit 56 detects whether the door segments 1, 1 are in the open positions or the closed positions along the track T. In a specific method for detecting the open/closed positions of the door segments 1, 1, the automatic door controller 4 is arranged to produce a pulse signal which corresponds to the positions of the door segments 1, 1 (i.e. open or closed). On receiving the pulse signal, the door position detection unit 56 is arranged to detect whether the door segments 1, 1 are in the open positions or the closed positions. For example, the number of pulses is set to 0 per unit time to indicate the fully closed state of the door segments 1, 1, whereas the number of pulses is set to 255 per unit time to indicate the fully open state of the door segments 1, 1. The automatic door controller 4 is arranged to output a gradually increasing number of pulses, as the door segments 1, 1 move from the fully closed state to the fully open state. With this arrangement, the door position detection unit 56 can accurately detect the open/closed positions of the door segments 1, 1.

[0050] The door position identification unit 57 receives an output signal from the door position detection unit 56. Based on the detected open/closed positions of the door segments 1, 1, the unit 57 identifies the positions of the door segments 1, 1 in the images. For example, as illustrated in FIG. 3(A), when the door segments 1, 1 are fully open, as indicated by an output of 255 pulse waves, the edge positions of the door segments 1, 1 on the images are identified at the points P2, P2. Turning to FIG. 3(B), when the door segments 1, 1 are fully closed, as indicated by an output of no pulse, the edge positions of the door segments 1, 1 on the images are identified at the point P3. In other words, when the number of pulses is 255, the unit 57 recognizes the objects locating at the points P2, P2 as the door segments 1, 1. Likewise, when the number of pulses is 0, the unit 57 recognizes the objects locating at the point P3 as the door segments 1, 1.

[0051] The judgement unit 58 receives outputs from the object height/position detection unit 55 and the door position identification unit 57. Then, the unit 58 judges whether each object observed in the taken images is the door segment 1 or an object other than the door segment 1. In this operation, the judgement unit 58 recognizes the presence of an object which locates higher than the floor 6, based on the information from the object height/position detection unit 55. In addition, the unit 58 recognizes the current positions of the door segments 1, 1, based on the information from the door position identification unit 57. In other words, among the objects which locate higher than the floor 6, the objects locating at the current positions of the door segments 1, 1 are recognized as the door segments 1, 1. Based on this recognition, the judgement unit 58 detects the presence or absence of any other object than the door segments 1, 1, and eventually determines whether an object to be detected (e.g. a person) is present in the image pickup area.

[0052] As described above, the floor detection unit 54, the object height/position detection unit 55, the door position detection unit 56, the door position identification unit 57 and the judgement unit 58 constitute object identification means 5B of the present invention.

[0053] The output unit 59 receives an output from the judgement unit 58. If the images of the predetermined area include any object which is neither the floor 6 nor the door segments 1, 1, the output unit 59 produces an object detection signal to the automatic door controller 4. In response to this signal, the automatic door controller 4 controls a driving motor for the door opening/closing mechanism, so as to keep the door segments 1, 1 in the open state or to open the closing or closed door segments 1, 1.

[0054] The object detection operation of this auxiliary safety sensor 5 takes place in the following manner.

[0055] To begin with, in the test operation of an automatic door, the area vertically under the cameras 51, 52 is cleared of any object except the floor 6. In this situation, the distance measurement unit 53 measures the distance to an object which is present vertically under the cameras 51, 52, based on the image information from the cameras 51, 52. Then, the unit 53 detects a point which locates vertically under the cameras 51, 52 in the images (the point P1 in FIG. 3 and FIG. 4). Then, the floor detection unit 54 is made to recognize any object as the floor 6, as far as such object locates at the same height and position as the point P1.

[0056] During the normal operation of the automatic door after the test operation, the cameras 51, 52 take images of the predetermined image pickup area which covers the track T of the door segments 1, 1, at fixed time intervals. Information on the taken images is sent to the distance measurement unit 53, where the distance between the cameras 51, 52 and each object in the images taken by the cameras 51, 52 is measured by the stereo image processing of these images as detailed above. The object for which the distance is measured is understood to include not only a person and like object, but also the floor 6, the door segments 1, 1, etc.

[0057] The data on the measured distance to each object is sent to the object height/position detection unit 55. The unit 55 detects the height and position of all objects in the taken images, except the floor 6 whose position is already recognized by the floor detection unit 54. Namely, among the objects in the images, the object height/position detection unit 55 fetches information which solely relates to any object locating at a different height or position relative to the position-recognized floor 6, and acquires the information on the height and position of the object.

[0058] On the other hand, the door position detection unit 56 detects whether the door segments 1, 1 are in the open positions or the closed positions along the track T., based on the number of pulses generated by the automatic door controller 4. On receiving the output signal from the door position detection unit 56, and based on the detected open/closed positions of the door segments 1, 1, the door position identification unit 57 identifies the positions of the door segments 1, 1 in the images. For example, as illustrated in FIG. 3(A), when the door segments 1, 1 are fully open, the edge positions of the door segments 1, 1 on the images are identified at the points P2, P2. Turning to FIG. 3(B), when the door segments 1, 1 are fully closed, the edge positions of the door segments 1, 1 on the images are identified at the point P3.

[0059] After these operations, the judgement unit 58 receives outputs from the object height/position detection unit 55 and the door position identification unit 57. Then, the unit 58 judges whether each object observed in the taken images is the door segment 1 or an object other than the door segment 1. In this manner, the unit 58 judges whether an object to be detected (e.g. a person) is present in the image pickup area. If the presence of a person or like object (an object other than the floor 6 and the door segments 1, 1) is recognized, a judgement signal is transmitted from the judgement unit 58 to the output unit 59. In response to this signal, the output unit 59 outputs an object detection signal to the automatic door controller 4. On receiving the object detection signal, the automatic door controller 4 either keeps the door segments 1, 1 in the open state, or opens them against the closing motion or from the closed state.

[0060] As described above, the sensor of the present embodiment is arranged to measure the distance between the cameras 51, 52 and each object observed in the images which are taken by the cameras 51, 52 covering a predetermined area around the door. This information is utilized for judgement of the presence or absence of any object except the floor 6 and the door segments 1, 1. In the case where an object other than the floor 6 and the door segments 1, 1 is observed in the images, the door segments 1, 1 are either kept in the open state, or made to open against the closing motion or from the closed state. Hence, the present embodiment can extend the detectable range of the sensor, as opposed to the conventional beam sensors. Besides, for the identification of the presence or absence of an object, the sensor of the present embodiment considers the information which excludes the one relating to the door segments 1, 1. Therefore, even if the door segments 1, 1 are observed in the taken images, the sensor ensures a reliable object detection operation, without mistaking the door segments 1, 1 for a person or like object. As a result, it is possible to enhance the reliability of the opening/closing action by the automatic door.

[0061] As a modified embodiment, the distance between the cameras 51, 52 and an object can be measured in a different manner. In this modification, the image pickup means is constituted with a camera having a variable focus lens. When this camera takes an image, the image information is sent to the distance measurement unit 53. The distance measurement unit 53 measures the distance to the object, based on the degree of focus on the object which is observed in the image taken by the camera.

[0062] Another modified embodiment relates to the means for detecting whether the door segments 1, 1 are in the open positions or the closed positions. In this modification, the door position detection means 56 detects the positions of the door segments 1, 1 (i.e. open or closed), based on the images taken by the cameras 51, 52. Referring to FIG. 3(A), while the door segments 1, 1 are closing from the fully open state in the directions of arrows, the edge positions of the door segments 1, 1 are displaced as shown by dash-dotted lines in FIG. 3(A). At the same time, provided that the images are viewed as a two-dimensional plane, the inclination angle to these edges varies as well. Accordingly, it is possible to detect the positions of the door segments 1, 1 (i.e. open or closed), by recognizing the edges of the door segments 1, 1 on the images, together with the positions and inclination angle of these edges.

[0063] As far as the above embodiments are concerned, the sensor for automatic doors according to the present invention is applied as an auxiliary safety sensor, but the present invention should not be limited to such application. Additionally, the sensor for automatic doors according to the present invention can combine the functions of the auxiliary safety sensor and the activation sensor, by extending the region to be covered by the cameras 51, 52. As shown in FIG. 5 (a view equivalent to FIG. 1), the sensor has an enlarged image pickup region, thereby combining the functions of the auxiliary safety sensor and the activation sensor.

[0064] With regard to this structure, the detection area of an activation sensor (not shown) is set on the interior and exterior of the doorway 2. An activation sensor circuit 50 for this activation sensor is built into the auxiliary safety sensor 5. When a person or the like enters the detection area of the activation sensor, the activation sensor circuit 50 detects the object, based on the outputs from the cameras 51, 52. Following the object detection, the activation sensor circuit 50 sends an object detection signal to the automatic door controller 4, so as to start the driving motor of the door opening/closing mechanism and open the door segments 1, 1. On the other hand, the auxiliary safety sensor 5 performs the same operations as mentioned above. Thus, the sensor can function as both the auxiliary safety sensor and the activation sensor.

[0065] The present invention is applicable not only to bi-parting automatic doors, as in the above embodiments, but also to single-sliding automatic doors.

[0066] In the above embodiments, the background object is defined as the floor 6, because the cameras 51, 52 are mounted on the transom 3 and have their image pickup direction oriented substantially downwards. Alternatively, the present invention may be arranged to mount the cameras near the floor, with the image pickup direction oriented substantially upwards. In this case, a ceiling or a wall is regarded as the background object.

[0067] The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

[0068] The present application is based on Japanese Patent Application No. 2001-51502, the content of which is incorporated herein by reference. In addition, the documents cited in this specification are incorporated herein by reference in its entirety. 

What is claimed is:
 1. A sensor for automatic doors which comprises: means capable of taking an image of a predetermined area around a door; means for measuring a distance between the image pickup means and each object observed in the taken image of the predetermined area, the distance measurement means operating on receiving an output from the image pickup means; means for identifying the presence of an object which is neither a background object nor the door, the object identification means operating on receiving an output from the distance measurement means, wherein each object for which the distance from the image pickup means is measured is identified as a background object or an object other than the background object, based on the measured distance, and wherein the object other than the background object is identified as the door or an object other than the door; and means for outputting an object detection signal, the output means operating on receiving an output from the object identification means, wherein the object detection signal is produced, with a proviso that the object which is neither the background object nor the door is observed in the taken image of the predetermined area.
 2. A sensor for automatic doors which comprises: means capable of taking an image of a predetermined area which covers a track of a door; means for measuring a distance between the image pickup means and each object observed in the taken image of the predetermined area, the distance measurement means operating on receiving an output from the image pickup means; means for detecting a floor and a height and position of the floor, the floor detection means operating on receiving an output from the distance measurement means, wherein the floor is detected from any object for which the distance from the image pickup means is measured; means for detecting a height and position of an object other than the floor, the object height/position detection means operating on receiving outputs from the distance measurement means and the floor detection means, wherein the object other than the floor is an object which is observed in the image taken by the image pickup means covering the predetermined area and which locates at a different height and position relative to the height and position of the floor; means capable of detecting whether the door is in an open position or a closed position along the track; means for identifying a position of the door on the image, the door position identification means operating on receiving an output from the door position detection means, based on the detected position of the door; means for judging whether the object which is observed in the taken image of the predetermined area and which is other than the floor is the door or an object other than the door, the judgement means operating on receiving outputs from the object height/position detection means and the door position identification means; and means for outputting an object detection signal, the output means operating on receiving an output from the judgement means, wherein the object detection signal is produced, with a proviso that the object which is neither the floor nor the door is observed in the taken image of the predetermined area.
 3. A sensor for automatic doors according to claim 1 or 2, wherein the sensor is associated with means for controlling an open/close drive of the door along the track, wherein the output means is capable of outputting the object detection signal to the door drive control means, such that the object detection signal outputted to the door drive control means causes the door to open fully.
 4. A sensor for automatic doors according to claim 1, 2 or 3, wherein the image pickup means has a plurality of image pickup elements; and wherein the distance measurement means measures the distance to each object by stereo image processing which utilizes parallax of images taken by these image pickup elements.
 5. A sensor for automatic doors according to claim 1, 2 or 3, wherein the image pickup means has a variable focus lens; and wherein the distance measurement means measures the distance to each object, based on the degree of focus on the object which is observed in the image taken by the image pickup means.
 6. A sensor for automatic doors according to claim 2, wherein the sensor is associated with means for controlling an open/close drive of the door along the track, the door drive control means producing an output signal which corresponds to the position of the door, wherein the door position detection means is capable of receiving the output signal from the door drive control means, and arranged to detect whether the door is in the open position or the closed position, based on the received output signal.
 7. A sensor for automatic doors according to claim 2, wherein the door position detection means is arranged to detect whether the door is in the open position or the closed position, based on the image taken by the image pickup means. 